1. Field of the Invention
The present invention relates in general to a method of fabricating a composite type magnetic head core, and more particularly to a method advantageously used for fabricating such a composite magnetic head core suitable for use with a recording medium having a high coercive force.
2. Discussion of the Prior Art
In the art of information recording and reproduction, it is known that the density of recording of information per unit area of a magnetic recording medium may be increased with an increase in the coercive force (Hc) of the medium. However, the recording on such a magnetic recording medium having a high coercive force requires a relatively high strength of a magnetic field produced by a leakage flux of a magnetic head. A ferrite material used for a magnetic head core presently available has a saturation magnetic flux density (Bs) which ranges from 4000 G (gauss) to 5000 G, whereby the recording magnetic field strength is more or less limited. Therefore, the currently available magnetic head core is not sufficiently capable of effecting a high-density recording, where the coercive force of the magnetic recording medium exceeds 1000 Oe (oersted).
A recently proposed solution to the above problem is the use of a composite type, so-called "metal-in-gap" magnetic head core wherein a magnetic film with a suitable thickness consisting of a metallic magnetic material is interposed between opposite surfaces of a ferrite material which define a magnetic gap therebetween. Such a metallic magnetic material, which may be a crystalline alloy such as Fe-Al-Si alloy (Sendust) or Ni-Fe alloy (Permalloy), or a non-crystalline alloy, is applied to at least one of the opposite ferrite surfaces defining the magnetic gap, for improving the recording characteristic of the head core when used with a high coercive force medium.
Conventionally, the composite, metal-in-gap magnetic head core of the type described above is produced in the following manner. That is, a first and a second ferrite blocks are butted and joined together so as to form an annular magnetic path, and define a magnetic gap therebetween. More particularly, the joining surfaces of these first and second ferrite blocks are initially mirror-finished, and a magnetic layer or film consisting of a metallic magnetic material is applied to at least one of the joining surfaces. Then, the two ferrite blocks are joined together at the joining surfaces, with a suitable bonding material such as a glass, to prepare an integral ferrite structure having a magnetic gap in which the metallic magnetic material exists. The thus prepared ferrite structure is cut at appropriate positions, to produce a desired composite metal-in-gap magnetic head core (head core slider).
In the method described above, the first and second ferrite blocks are joined together at an elevated temperature, and internal thermal stresses occur in the ferrite material providing the core body and the metallic magnetic material applied to the magnetic gap defining surface of the ferrite, since these two materials have a relatively large difference in coefficient of thermal expansion (for example, 110-120.times.10.sup..differential. in the case of a ferrite, and 140-150.times.10.sup.7 in the case of Sendust). In this condition, the ferrite structure is subsequently subjected to a cutting or machining operation to produce a suitably shaped head core. At this time, the metallic magnetic layer or film is cut with the ferrite material, and tends to be separated or removed from the ferrite surface to which the layer or film is bonded. Further, the machining operation may cause cracking of the ferrite portion adjacent to the metallic magnetic layer. These structural defects undesirably lead to a relatively low yield ratio of the magnetic head core, and reduced operating stability and reliability of the produced head core. Thus, the conventional method suffers from a potential problem that should be solved.